Stupid RF newbie has a question...

[Dave]

Well, I probably knew this at one time, but then I went into the business of
repairing computers and associated equipment (simple troubleshooting and
board-swapping) and did that for 12 years before sleeping for the last ten
(with a sleep disorder). Now I find I have forgotten everything but Ohm's
Law (and am beginning to wonder about that.) So, I have some questions...

Recently bought a copy of Introduction to Radio Frequency Design (Hayward)
and discovered just how ignorant I am now. In the first few pages there are
a couple of symbols I don't recognize. The first is simply an ampersand (&
symbol) but it's between a couple of variables in an equation. What is that
called in this capacity, and where should I look to find out what it means
(again, in this capacity.) The second is simply two vertical lines in
parrallel, rather like the side-bars of a capital H but without the
cross-bar in the middle. Again, what is this called and where should I look
for information on it? (Maybe a capital pi symbol? But what does it
*mean*?) This last reminds me of the three dots in a small triangle, used
in logic to mean "therefore," but I don't even remember where to look to
check out that possibility. Totally ignorant. (Shaking head.)

Thanks in advance for any help. I really hate to admit being this stupid,
but I need to know, so...

Dave
[email protected]

 

[Tim Wescott]

Well, I probably knew this at one time, but then I went into the business of
repairing computers and associated equipment (simple troubleshooting and
board-swapping) and did that for 12 years before sleeping for the last ten
(with a sleep disorder). Now I find I have forgotten everything but Ohm's
Law (and am beginning to wonder about that.) So, I have some questions...

Recently bought a copy of Introduction to Radio Frequency Design (Hayward)
and discovered just how ignorant I am now. In the first few pages there are
a couple of symbols I don't recognize. The first is simply an ampersand (&
symbol) but it's between a couple of variables in an equation. What is that
called in this capacity, and where should I look to find out what it means
(again, in this capacity.) The second is simply two vertical lines in
parrallel, rather like the side-bars of a capital H but without the
cross-bar in the middle. Again, what is this called and where should I look
for information on it? (Maybe a capital pi symbol? But what does it
*mean*?) This last reminds me of the three dots in a small triangle, used
in logic to mean "therefore," but I don't even remember where to look to
check out that possibility. Totally ignorant. (Shaking head.)

Thanks in advance for any help. I really hate to admit being this stupid,
but I need to know, so...

Dave
[email protected]

What pages? What equation numbers? I don't see this is my copy ("first
ARRL edition").

The only place I know where an ampersand is used between variables is in
computer languages related to C where it means "and" (either bitwise or
logical depending on the language). A vertical bar, "|", in C means
bitwise or and two "||" mean logical or -- but that doesn't go in an RF
book!

Two vertical lines placed closely between two impedances often mean
those impedances taken in parallel, so if R1 and R2 are both 100 ohms
then R1+R2 = 200 ohms, and R1 || R2 = 50 ohms. _This_ I could believe
seeing. Pairs of vertical lines bracketing a vector quantity, ||x||
mean the vector "norm", usually the sum of the square of its elements,
but sometimes something different if the mathematician in question
notices that you seem to be understanding the material -- and I wouldn't
expect it in Hayward's book.

Three dots in a small triangle does indeed mean "therefore". Sometimes
you'll see two horizontal parallel lines with an arrowhead, like "=>",
that technically means "it follows" but is used as "therefore",
particularly on blackboards where the three dots are hard to write...

 

[Terry Pinnell]

In the first few pages there are
a couple of symbols I don't recognize. The first is simply an ampersand (&
symbol) but it's between a couple of variables in an equation.

Without seeing the context, impossible to be sure. But my first guess
would be a logical AND. Is it something like 'A&B' or 'X&Y', and were
logic signals being discussed?

The second is simply two vertical lines in
parrallel, rather like the side-bars of a capital H but without the
cross-bar in the middle.

With the same caveat about context, that normally means 'in parallel'.
So for example 'Ra||Rb' would mean the two resistors Ra and Rb in
parallel. And '8||8' would be 4 if the context was resistance, or 16
if capacitance.

 

[Paul Burridge]

Well, I probably knew this at one time, but then I went into the business of
repairing computers and associated equipment (simple troubleshooting and
board-swapping) and did that for 12 years before sleeping for the last ten
(with a sleep disorder). Now I find I have forgotten everything but Ohm's
Law (and am beginning to wonder about that.) So, I have some questions...

Snip!

There are several sites on the web that provide the info you seek.
Just try Googling under "mathematical symbols" and you'll be spoilt
for choice.

 

[Dave]

What pages? What equation numbers? I don't see this is my copy ("first
ARRL edition").

The only place I know where an ampersand is used between variables is in
computer languages related to C where it means "and" (either bitwise or
logical depending on the language). A vertical bar, "|", in C means
bitwise or and two "||" mean logical or -- but that doesn't go in an RF
book!

Two vertical lines placed closely between two impedances often mean
those impedances taken in parallel, so if R1 and R2 are both 100 ohms
then R1+R2 = 200 ohms, and R1 || R2 = 50 ohms. _This_ I could believe
seeing. Pairs of vertical lines bracketing a vector quantity, ||x||
mean the vector "norm", usually the sum of the square of its elements,
but sometimes something different if the mathematician in question
notices that you seem to be understanding the material -- and I wouldn't
expect it in Hayward's book.

Three dots in a small triangle does indeed mean "therefore". Sometimes
you'll see two horizontal parallel lines with an arrowhead, like "=>",
that technically means "it follows" but is used as "therefore",
particularly on blackboards where the three dots are hard to write...

Shit. I really am an idiot. It wasn't in Haywards book at all, but was in
something I got off the net that I was studying along with Hayward's book.
Sorry. *Really* didn't mean to be *that* stupid.

What I described is in a PDF at the following website:
http://www.eng.fsu.edu/~ejaz/EEL3300L/lab8.pdf

The ampersand and verticle parrallel lines are on page 3. On page 1 is a
capital B and a large scripted f which I also wonder about. I assume the
capital B is for beta, but the f looks like something I would see in a
function declaration rather than an electronics equation. On page 2, down
near the bottom, is the same scripted f, this time in subscript to a V for
voltage. All of this is unfamiliar to me, and I would really appreciate any
help anyone could offer on it.

I apologize for the mistake of saying it was in Wes Hayward's book. I was
trying to study all of this spread out on a table while with my wife at her
office, and posted about it that night after getting home. Did not intend
to confuse the issue..

Thanks for trying to help.

Dave
[email protected]

 

[Dave]

Without seeing the context, impossible to be sure. But my first guess
would be a logical AND. Is it something like 'A&B' or 'X&Y', and were
logic signals being discussed?


With the same caveat about context, that normally means 'in parallel'.
So for example 'Ra||Rb' would mean the two resistors Ra and Rb in
parallel. And '8||8' would be 4 if the context was resistance, or 16
if capacitance.

Please see my reply to Tim Wescott for a clearer description of the context
and usage.

Thanks for the reply.

Dave
[email protected]

 

[Dave]

questions...

Snip!

There are several sites on the web that provide the info you seek.
Just try Googling under "mathematical symbols" and you'll be spoilt
for choice.

Could not find any of this, even with Google. Really beginning to wonder
now...

Dave
[email protected]

 

[Tim Wescott]

business of




Shit. I really am an idiot. It wasn't in Haywards book at all, but was in
something I got off the net that I was studying along with Hayward's book.
Sorry. *Really* didn't mean to be *that* stupid.

What I described is in a PDF at the following website:
http://www.eng.fsu.edu/~ejaz/EEL3300L/lab8.pdf

The ampersand and verticle parrallel lines are on page 3. On page 1 is a
capital B and a large scripted f which I also wonder about. I assume the
capital B is for beta, but the f looks like something I would see in a
function declaration rather than an electronics equation. On page 2, down
near the bottom, is the same scripted f, this time in subscript to a V for
voltage. All of this is unfamiliar to me, and I would really appreciate any
help anyone could offer on it.

I apologize for the mistake of saying it was in Wes Hayward's book. I was
trying to study all of this spread out on a table while with my wife at her
office, and posted about it that night after getting home. Did not intend
to confuse the issue..

Thanks for trying to help.

Dave
[email protected]

I think the ampersand is just that professor's confusing attempt to make
things clear (I read it as "R_1 in parallel with R_2, or R_B"), the
vertical parallel lines indicate resistors in parallel.

The "Bf" is forward beta, and is usually denoted with a real, actual
Greek letter beta and a subscripted 'f'; that guy really needs to learn
how to use an equation editor. The "V_f" (he actually managed a real
subscript that time!) is the forward diode drop of the transistor -- one
often just assumes a number like 0.65V and designs as if it won't
change, which works as long as you remember that it _does_ change with
temperature.

 

[Charles Schuler]

Tell us what you are trying to do. If you want to learn more about radio
frequencies, the ARRL handbook can't be beat.

 

[Dave]

I am wanting to build a simple RF amplifier to boost the signal to my
television, and then use the knowledge I gained in that project to build a
second RF amplifier to boost and filter the signals I receive on my
Shortwave radio (which I connect to a random-wire antenna up on the roof.)
I have a background in electronics (with the exceptions listed earlier) and
would like to keep on learning in this new direction. I do have a simple
workshop set up (again, after 20 years) and am basically seeking to pick up
the hobby again.

I realize I started out by making a fool of myself, but really am serious
and would appreciate any help anyone could offer.

Thanks,

Dave
[email protected]

 

[Paul Burridge]

Could not find any of this, even with Google. Really beginning to wonder
now...

Sigh...
Post this link into your browser:

http://whatis.techtarget.com/definition/0,,sid9_gci803019,00.html

 

[Dave]

Sigh...
Post this link into your browser:

http://whatis.techtarget.com/definition/0,,sid9_gci803019,00.html

Okay, yeah, I went there earlier and checked out (I thought) everything
there, but didn't see any of the symbols described, and didn't know how to
type them into the search field or what to call them. There *is* the
absolute value and "is parrallel" symbols, but those don't make any sense in
the context in which the symbols I am describing are used in the PDF
document I referrenced elsewhere. Example: Vin = Vcc(R2/R1+R2)&Rb = R1 II
R2. (There is no Rb in the circuit illustration, and R1 is *not* parrallel
with R2. R1 and R2 form what I think is called a bias stick, providing bias
voltage for the base of the transistor in the circuit.) The PDF article is
about biasing transistors, BTW. Am I missing something?

Thanks,

Dave
[email protected]

 

[Dave]

I think the ampersand is just that professor's confusing attempt to make
things clear (I read it as "R_1 in parallel with R_2, or R_B"), the
vertical parallel lines indicate resistors in parallel.

Well, that sounds plausible until you look at the circuit issustration over
the text. There is no Rb, and R1 and R2 are not in parrallel. Please see
my reply to Paul Burridge.

The "Bf" is forward beta, and is usually denoted with a real, actual
Greek letter beta and a subscripted 'f'; that guy really needs to learn
how to use an equation editor. The "V_f" (he actually managed a real
subscript that time!) is the forward diode drop of the transistor -- one
often just assumes a number like 0.65V and designs as if it won't
change, which works as long as you remember that it _does_ change with
temperature.

Okay, that I can see. Crap. Confusing.

Thanks for your help. Now if I can just figure the rest out...

Dave
[email protected]

 

[Charles Schuler]

I am wanting to build a simple RF amplifier to boost the signal to my
television, and then use the knowledge I gained in that project to build a
second RF amplifier to boost and filter the signals I receive on my
Shortwave radio (which I connect to a random-wire antenna up on the roof.)
I have a background in electronics (with the exceptions listed earlier)
and
would like to keep on learning in this new direction. I do have a simple
workshop set up (again, after 20 years) and am basically seeking to pick
up
the hobby again.

Wideband RF amplifiers are not a beginner's project. Not trying to
discourage you, but to cover 54 to 800 MHz with decent noise performance and
gain is not easy. If you want to boost one channel (or so) that's more
manageable. Short wave covers 2 to 30 MHz and many preamps are already out
there. By the way, the sensitivity of many modern receivers is such that
little can be gained (pun) with a preamplifier. Ramsey electronics might
have some kits. Nothing wrong with kits for a beginner. Also, you can
Google for some schematics.

Again, the ARRL handbook is a gem if you really want to learn RF.
Electronics can be a fun hobby. It's just not as easy as it once was to
come up with anything significant at home.

 

[Dave]

Wideband RF amplifiers are not a beginner's project. Not trying to
discourage you, but to cover 54 to 800 MHz with decent noise performance and
gain is not easy. If you want to boost one channel (or so) that's more
manageable. Short wave covers 2 to 30 MHz and many preamps are already out
there. By the way, the sensitivity of many modern receivers is such that
little can be gained (pun) with a preamplifier. Ramsey electronics might
have some kits. Nothing wrong with kits for a beginner. Also, you can
Google for some schematics.

Again, the ARRL handbook is a gem if you really want to learn RF.
Electronics can be a fun hobby. It's just not as easy as it once was to
come up with anything significant at home.

Hmm. I have a schematic I intend to follow for the SW part (MFJ 1020A) and
have already purchased the discrete components, but realized I don't know
much about actual construction, which is the basis of what I am wanting to
pursue. For the TV part, I am thinking only of channels 2-69, or something
like that. 54 - 450 Mhz is what I have in mind. The reasoning behind this
is that our old VCR gave us fantastic reception, but the new one doesn't
(same antenna but in a different location- it used to be mounted on the
carport, and is now in back.) I've been told repeatedly that VCR's don't
amplify the incoming signal, but that VCR did (signal quality dropped
significantly when I was taken out of the circuit.) For the TV RF amplifier
I am planning on using a couple of NTE10 VHF/UHF amplifiers, equivelant to
the 2SC3510. I figured I would come up with my own schematic after
digesting Wes Hayward's book, and perhaps Christopher Bowick's. (I have
time on my hands, and don't mind the research.) If you have a suggested
source for schematics I am all ears. For that matter, I'm all ears anyway.
I am just trying to pursue my old high-school hobby of tinkering and using
what I learn to build something usefull.

Thanks,

Dave
[email protected]

 

[Nicholas O. Lindan]

I am wanting to build a simple RF amplifier to boost the signal to my
You can buy a 4-output distribution amplifier for ~$25 (?) at Radio Shack.
This is useful to mitigate cable loss if you have a lot of TVs in your house.
It won't improve your reception.

'Building' an amplifier will teach you nothing but how to screw and solder.
Designing a wide-band RF amplifier for the VHF & UHF TV broadcast bands is
another
matter - a whole bunch of university level circuit design courses should about
do it. And you will need all sorts of very pricey RF instrumentation to
verify the design.

and then use the knowledge I gained in that project to build a
second RF amplifier to boost and filter the signals I receive on my
Shortwave radio (which I connect to a random-wire antenna up on the roof.)

A 'random wire' antenna? I had one of those when I was young, are they
mainstream nowadays?

A pre-amp will not help you receive signals. The only thing that will help
is a very _non-random_ set of antennas: an antenna for each band; directional;
rotatable; on the highest tower the zoning ordinance will let you get away
with; on the highest ground in the neighborhood.

Again, the ARRL handbook is a gem if you really want to learn RF.

Good idea. Start simple. Start in the 80 meter band where AOTE (Any
Old Test Equipment) will be adequate.

Get a novice license (do they still have novice licenses?).

 

[Rick]

Well, that sounds plausible until you look at the circuit issustration over
the text. There is no Rb, and R1 and R2 are not in parrallel. Please see
my reply to Paul Burridge.

R1 and R2 ARE in parallel for ac signals - each start off the same
point (the base) and go to a low-impedendace point (Vcc for R1,
GND for R2). That makes them in parallel.

I'm afraid the ampersand in this context just means "and". The author
was showing how to migrate from Circuit #2 to Circuit #3, and this
resulted in the two equations linking the components in Circuit #3
with the components in Circuit #2.

In Circuit #2, the base of the transistor "sees" Rb whereas in Circuit
#3 it sees R1 || R2. For circuits #2 and #3 to be equivalent, then,
we require Rb = R1 || R2 - and that's one of the equations he's listed.

To equate the DC voltages at the base in Circuits #2 and #3, he's
ignored the drop across Rb and said that in Circuit #2, the voltage
is Vin, whereas in Circuit #3, the voltage is Vcc divided down by
R1 and R2, ie Vcc * R2/(R1+R2) - and that gives you his second
equation, Vin = Vcc * R2/(R1+R2).
If you then solve the two equations he's shown (which happen to
be separated by an ampersand!), then you get:
R1 = Vcc * Rb / Vin
R2 = vcc * Rb / (Vcc - Vin)

 

[Terry Pinnell]

I am wanting to build a simple RF amplifier to boost the signal to my
television, and then use the knowledge I gained in that project to build a
second RF amplifier to boost and filter the signals I receive on my
Shortwave radio (which I connect to a random-wire antenna up on the roof.)
I have a background in electronics (with the exceptions listed earlier) and
would like to keep on learning in this new direction. I do have a simple
workshop set up (again, after 20 years) and am basically seeking to pick up
the hobby again.

I realize I started out by making a fool of myself, but really am serious
and would appreciate any help anyone could offer.

Thanks,

Dave

Tim and I already answered your specific question about '||'. That
means 'in parallel', and I gave some examples.

As for '&', now that I see the document, it plainly means simply
'and'! The formula was presumably badly typeset, and should have had a
blank space on both sides of the '&'.

But isn't that obvious from the context? I don't think you're being
careful enough in your reading. In your reply to Paul Burridge you
said: "There is no Rb in the circuit illustration, and R1 is *not*
parrallel with R2."

Directly above the formula in question, the author says:
"The Thevnin equivalent of VCC, R1 and R2 in circuit # 3 is Vin and Rb
in circuit # 2." If you scroll back up to Circuit 2, which you
presumably read earlier, you'll see Rb.

Note that some care is needed when using symbols like 'RB'; in his
Circuit 2 the 'B' is actually a little smaller than the 'R', but it's
not well-positioned. I'd have written 'Rb'. That's particularly
sensible when you have no subscript symbols available, as is the case
in these newsgroup threads.

As for R1 || R2, Thevenin is about *equivalences*. Presumably you've
read up on his Theorem? (One of hundreds of relevant links is:
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/thevenin.html )

So, the 'R1||R2' part of the formula is meant to be read as 'the value
of R1 and R2 in parallel.

The author has also consistently mis-spelt 'Thevenin'.

 

[Rich Grise]

Okay, yeah, I went there earlier and checked out (I thought) everything
there, but didn't see any of the symbols described, and didn't know how to
type them into the search field or what to call them. There *is* the
absolute value and "is parrallel" symbols, but those don't make any sense
in the context in which the symbols I am describing are used in the PDF
document I referrenced elsewhere. Example: Vin = Vcc(R2/R1+R2)&Rb = R1 II
R2. (There is no Rb in the circuit illustration, and R1 is *not*
parrallel
with R2. R1 and R2 form what I think is called a bias stick, providing
bias
voltage for the base of the transistor in the circuit.) The PDF article
is
about biasing transistors, BTW. Am I missing something?

Um, please don't slap me, but I think the ampersand means, "and", and the
"in parallel" sign means "in parallel". It's a sentence, telling you that
the voltage at Vin is voltage-divided from Vcc by R1 and R2, and the
effective base input resistance for the signal is the value of the two
resistors in parallel, because from the signal's POV, Vcc and ground are
the same point. This would be the "input impedance" of the circuit, which
is the load seen by the driving source.

Well, that's a seat-of-the-pants kinda guy's description.

Hope This Helps!
Rich

 

[Rich Grise]

[please snip better!]

Okay, that I can see. Crap. Confusing.

Thanks for your help. Now if I can just figure the rest out...

There might be something in here that might help:
http://www.google.com/search?q=thevenin+equivalent&btnG=Search+the+Web

Good Luck!
Rich